The present invention relates to mechanical heart valve prostheses. More specifically, the invention relates to a driver tool for attaching and implanting heart valve prostheses.
Implantable mechanical heart valves are used for replacement of defective valves in hearts of patients. One common implantation method employs a sewing ring or suture cuff which is attached to and extends around the outer circumference of the mechanical valve orifice. The sewing cuff is made of a biocompatible fabric suitable for allowing a needle and suture to pass therethrough. The cuffs are typically sutured to a tissue annulus that is left when the surgeon removes the native valve from the patient""s heart. The sutures are tied snugly, thereby securing the valve to the heart.
Sewing cuffs are labor intensive, difficult to manufacture and are difficult to secure to the valve orifice. Further, suturing the cuff to the tissue annulus is time consuming and cumbersome. The complexity of suturing requires a patient to be on cardiopulmonary bypass for a lengthy period. It is also desirable to provide a large lumen through the valve orifice relative to the overall valve diameter for blood flow. However, techniques for attaching the sewing cuff to the valve orifice typically require that the area of the valve lumen be reduced to accommodate an attachment mechanism. For example, the sewing cuff is typically retained between two rims of the valve orifice. One of the rims normally defines the outside diameter of the valve orifice and thus limits the size of the valve lumen.
Another technique for attaching heart valves uses a series of pins which pierce the tissue annulus of the heart. The pins are crimped or bent, thereby locking the valve to the heart tissue and preventing the valve from separating from the heart. This technique is described in U.S. Pat. Nos. 3,574,865 and 3,546,710. Another technique for attaching a prosthetic heart valve to the heart tissue is shown in U.S. Pat. No. 4,705,516 in which an outer orifice ring is sutured to the tissue annulus and an inner orifice ring is then screwed into the outer orifice ring. However, the rings are not locked together and may become unscrewed after extended use.
Implantable heart valves can also use helical fasteners to hold them securely to surrounding tissue in the body. The use of helical fasteners or screws is disclosed in the above cited application Ser. No. 09/062,822. However, access to the multiple helical fasteners used with an implant tool one at a time can be difficult and time consuming. The fasteners face in different directions and a simple tool must be positioned multiple times to approach the implantable heart valve component from several difficult angles around the heart, some of which may be obstructed by adjoining tissue. A tool which solves this problem and simultaneously drives multiple fasteners using satellite gears is disclosed in U.S. Pat. No. 6,074,418. This simultaneous driver tool, however, is limited in the number of fasteners that can be driven conveniently. As the number of fasteners increases, the number of satellite gears increases as well, and the satellite gears must be made smaller to fit all of them in the tool housing. There is a minimum gear tooth size that will allow sufficient mechanical contact between the central gear and the satellite gears. Consequently, there is a minimum satellite gear diameter, which means there is a maximum number of gears that will fit in the tool housing diameter. Also, the gear ratio or mechanical advantage for the tool decreases as the satellite gears get smaller and the torque needed to drive the fasteners increases.
In some applications, however, a greater number of fasteners is desired to distribute the securing forces over a larger number of fasteners to lower concentrations of securing force in the small portions of tissue annulus engaged by each of the helical fasteners, without adversely affecting the mechanical advantage of the tool. In some applications, a greater number of fasteners is desired to decrease the spacing between attachment points.
The present invention is useful in implanting a prosthetic heart valve in a heart with fasteners. The heart valve includes an outer ring for coupling to a tissue annulus of a heart. An inner orifice ring includes an occluding mechanism movable between an open position, which allows blood flow through the lumen, and a closed position which prevents blood flow through the lumen. The inner orifice ring is adapted to be coupled to the outer orifice ring after the outer orifice ring has been attached to the tissue annulus.
The outer ring is attached to the tissue annulus by helical fasteners and is coupled to the inner orifice ring by a snap fit.
In the present invention, a driver tool drives multiple fasteners simultaneously through the outer ring of a heart valve component into the surrounding tissue annulus of a heart.
The driver tool includes a tool housing that has a distal housing end couplable to the heart valve component and has a proximal housing end spaced away from the distal housing end along an axis.
The driver tool includes a central shaft in the tool housing that has a proximal shaft end that can be coupled to a driving force such as an electric motor or an operator""s hand. The central shaft extends to a distal shaft end near the heart valve component.
The driver tool includes a first satellite gear drive layer that has a first drive gear engaging the distal shaft end and a first plurality of satellite gears at first spaced circumferential positions meshing with the first drive gear. The first satellite gear drive layer also has a first plurality of flexible shafts connected to the first plurality of satellite gears and adapted to drive a first portion of the fasteners.
The driver tool also includes a second satellite gear drive layer that has a second drive gear engaging the distal shaft end and a second plurality of satellite gears at second spaced circumferential positions meshing with the second drive gear. The second satellite gear drive layer also has a second plurality of flexible shafts connected to the second plurality of satellite gears and arranged to drive a second portion of the fasteners.
Preferably, a first (lower) plurality of satellite gears are separated from one another by gaps, and the second (upper) plurality of satellite gears are circumferentially offset to align with the gaps in the first row. In this preferred arrangement, the second plurality of flexible shafts pass through the gaps, and each upper and lower flexible shaft drives a corresponding fastener simultaneously.